Fall Armyworms on the March

By Rick L. Brandenburg, North Carolina State University

Many insect pests attack turf. Sometimes you see them coming, sometimes you don't. Pests such as chinch bugs, mole crickets or white grubs usually occur in damaging numbers in specific — and often predictable — sites and times. While a persistent pest may not be all that desirable, there is something to be said for predictability.

By contrast, some of the most serious problems in turfgrass can be the result of sporadic, unpredictable pests. These are the pests that often catch us by surprise, and by the time we've figured out what the problem is, the damage has become serious. These are the pests that often provide the greatest challenge, particularly when timing of control is important.

The fall armyworm (Spodoptera frugipeda) is a good example of a pest that can sneak up on you. When it does, the results can be disastrous. Fall armyworms can strike in most regions of the United States and seem to have been relatively serious during the past few years. No one can accurately predict what this pest will do in coming years. However, if it does strike, you must learn two things. First, you should understand the pest's biology. Second, you need to know how to most effectively control them.

ARMYWORM LIFECYCLE

Unlike many turfgrass insect pests, the fall armyworm overwinters in just a few restricted areas. It is a tropical pest and capable of overwintering only in warm-winter areas. Obviously, then, this pest does not overwinter in most of the United States. Rather, its overwintering is restricted to southern Florida, southern Texas and a band along the Gulf Coast running inland about 100 miles. As a result, the fall armyworm is a more consistent threat to southern turf and a more sporadic pest as you go farther north.

Each spring, adults emerging in the South begin migrations northward. Adult moths have a wingspan of a little more than an inch and their front wings display a dark-gray mottled appearance with light and dark markings (see photo, page 22). A white marking that appears as a blotch near the tip of each front wing is a distinct characteristic.

In the South, three or more generations per year may occur. In the North, only one generation will occur. The caterpillars feed on a variety of plants. Notably, warm-season grasses such as bermudagrass, St. Augustinegrass and some others are commonly attacked. Among the cool-season grasses, bluegrass, ryegrass, fine fescue and bentgrass are preferred cool-season turfgrasses. Fall armyworms also attack corn, soybeans, small grains and a number of wild plants.

The moths lay eggs on a variety of surfaces, including turf, but often lay eggs on trees, shrubs, signs, flags, buildings and other light-colored surfaces. The moths are attracted to lights, so it's not uncommon for infestations to start near light sources. These eggs hatch in 7 to 10 days, when the small caterpillars spin down on silky threads and begin to feed on foliage. As they grow, they will feed on all above-ground portions of the turfgrass. The caterpillars will feed for 2 to 4 weeks depending on temperatures. Damage often appears along the edge of the turf and moves across the sward. Most of the noticeable damage is caused by larger caterpillars. Fall armyworms sometimes move as a group, hence the name “armyworm.”

Fully grown, armyworms are about 1.5 inches long. They range in color from olive green to light tan, to nearly black, typically with light stripes that run the length of the body. An inverted “Y” is present on the front of the head of the caterpillar.

After feeding, the caterpillars pupate in the soil. After about 2 weeks in the soil, the moths emerge and the next generation begins. In the extreme South, four or more generations are possible. In the North, one generation late in the summer or early fall is all that will occur.

MONITORING ARMYWORMS

Feeding damage often is first noticed as blades of grass begin to appear transparent. Non-stoloniferous turfgrasses, such as tall fescue, are damaged more severely.

One of the most common indicators of a fall armyworm infestation is the presence of a large number of birds on or near the turf. If you see this, you should be suspicious of an insect problem. Pheromone traps specific for armyworms are available from commercial sources (see photo, page 20). These traps work by luring the moths with the pheromone. Once they enter the trap, they are entangled in an adhesive. If you place these traps near turf areas and large numbers of the moths are captured prior to the egg-laying period, this may be an early indication of an impending problem. However, you still need to monitor for the actual infestation.

An effective tool for monitoring the abundance of the turf-inhabiting caterpillars, including fall armyworms, is to use a soapy water flush. This technique utilizes a solution of liquid dishwashing detergent and water. Add about 2 tablespoons of detergent in 2 gallons of water and pour it slowly over about 1 square yard. Keep observing the area for about five minutes after applying the soapy water. Caterpillars often come to the surface and then stop moving. If you apply the soapy water and leave, only to return five minutes later, you might not see some of the armyworms that have emerged.

MAKING A TREATMENT DECISION

Once you know that a potentially damaging population exists, you have a treatment decision to make. The mere presence of fall armyworms does not alone justify treatment. However, visible damage and “droppings” from the caterpillars are clues that a problem is occurring. At least five to six caterpillars per square yard are required to visibly damage most well-maintained turf. Therefore, populations exceeding six to eight worms per square yard would be considered threatening and warrant treatment.

If the armyworms are small (less than 0.5 inch long), they may not have caused any significant damage yet, but rest assured they will grow and represent a serious threat over the next two weeks. Larger caterpillars (more than 1 inch long) may be causing serious damage already. However, keep in mind they may also be near the end of the larval life stage and may be pupating in the soil in a few days. In other words, the damage may already be done.

Fall armyworms are usually more severe in abnormally dry summers because many plant hosts may dry up, forcing the caterpillars to seek out irrigated turf for food. Wet, cool springs also seem to increase problems with this pest, possibly due to detrimental effects this type of weather has on natural enemies of the fall armyworm.

Fall armyworms seem to be especially troublesome in certain specific situations. For example, newly seeded, sodded and sprigged turf areas appear to be quite vulnerable to fall armyworms. Such turf must be monitored closely.

CONTROL STRATEGIES

Effective control can be fairly simple if you take steps while the caterpillars are still small. This prevents visible damage and most products are more effective against smaller worms. Finding the worms at this stage requires some vigilance. Because this pest is generally a sporadic one, you simply can't use the soapy water drench everywhere. As I mentioned, the presence of birds in a turf area is often a good indicator. If you see lots of birds, start checking immediately for caterpillars.

While the smallest caterpillars may feed at any time during the day, larger ones feed more often late in the day and early in the morning. For this reason, your treatment may be more effective if you apply it late in the day. It also may increase the level of control if you avoid mowing and irrigating the turf for a day or two after treatment. This keeps the insecticides on the blades of grass where the caterpillars will feed. As a general rule, spray formulations provide a higher level of control than granular formulations. (However, this is not necessarily true of all products.)

Fall armyworms are a little more difficult to kill than cutworms and as the worms become larger, the challenge becomes greater. Many turf managers rely on pyrethroids for control of armyworms, but other chemicals are effective as well (see table, page 21).

The damage creates a frosted appearance or a brown area (look for this symptom late in the summer or early fall) or in the case of severe infestation, the turf may be completely denuded. Fall armyworms rarely kill the turf, even if left untreated, but they can make it look very unsightly. Damage usually moves in from the edges and often proceeds in a relatively straight line as the armyworms “march” across the turf area. This line may progress at 1 to 3 feet per night.

The sporadic nature of fall armyworms creates the biggest challenge. Knowing that in most areas they only occur late in the summer is of some help. (Except in the South, where they can occur most times of the year.) Frequent scouting, pheromone trapping and a watchful eye can help keep you alert to the need to check an area with soapy water.

Dr. Rick L. Brandenburg is professor of turfgrass entomology at North Carolina State University (Raleigh, N.C.).

CONTROLS, OLD & NEW

The list of insecticides on page 21 includes several traditional products such as isofenphos (Oftanol), chlorpyrifos (Dursban), acephate (Orthene, Ketch) and carbaryl (Sevin). Many expect these products to lose more of their registered uses (in addition to those already lost) as carbamates and OPs are reevaluated under Food Quality Protection Act (FQPA) provisions. Pyrethroids are considered to be effective replacements for these products. Biologicals also give us some effective products, including the tried-and-true Bacillus thuringiensis products, and some relatively new materials as well. Two notable synthetic products are spinosad, an insect growth regulator, and halofenozide, better known as a grub control but also effective against armyworms.

AT WAR WITH ARMYWORMS

Greg Orlacchio, owner of Turf Works in Farmingdale, New Jersey, boasts some high-profile names among his clientele, including rocker Jon Bon Jovi. Such upscale customers demand the highest level of results and often won't tolerate the sight of a single insect.

July 2001 provided a little extra excitement for Orlacchio. Maintaining golf-course-caliber lawns for very particular customers is difficult enough when things go well. But when an unwelcome visitor arrived last year, Orlacchio had a real challenge on his hands.

Armyworms invaded in huge numbers and threatened to chew New Jersey's most beautiful lawns into oblivion. Orlacchio's service area of exclusive central Jersey shore communities was right in the middle of the “war zone.” Orlacchio, who's been in business for 25 years, had never seen anything like it. “There were so many worms that the ground seemed to be moving. In some neighborhoods, they were literally marching in the streets,” Orlacchio said. “People were scooping them up with snow shovels.”

The worms appeared suddenly and were reducing lawns to the dirt within days. “A typical scenario would be that a lawn was alright on Sunday and ruined by Thursday,” he explained. It didn't take Orlacchio long to realize the seriousness of the problem. He had to get to all of his customers as quickly as possible, and that meant treating 10 million square feet within a week.

Orlacchio had relied on Dursban in the past. However, like all LCOs, he's had to consider alternatives due to the impending loss of chlorpyrifos and other organophosphate (OP) insecticides. Pyrethroids are often cited as replacements for OPs, so Orlacchio decided to try deltamethrin, Chipco's DeltaGard. He'd already had successes with this product in other situations, so he felt comfortable using it in such a critical circumstance.

He and his staff worked 10-hour days treating lawns, and the insecticide's quick knock-down made their work pay off. “We knew a pyrethroid was the thing to use because it's fast,” Orlacchio said. After treating all his customers' lawns, Orlacchio worried that a second generation was on its way. It was a possibility, he knew, but the rest of the summer played out quietly. “It was a once-in-a-lifetime occurrence, we hope,” Orlacchio reflects.

COMPANY PROFILE

Company name - Turf WorksOwner - Greg OrlacchioFounded - 1980Employees - 6Accounts serviced - 800Headquarters - Farmingdale, New JerseyBackground - Orlacchio started the company as a lawn service business while he was in collegePrimary services - Weed and insect control for residential and commercial properties